1. Field of the Invention
The present invention relates to ophthalmic lenses such as, for example, contact lenses or intraocular lenses (IOLs). Exemplary embodiments include monofocal and multifocal diffractive ophthalmic lenses having reduced light scatter and/or improved light energy distribution, for example through subtle shaping of echelettes with appropriately curving profiles.
2. Description of Background Art
Presbyopia is a condition that affects the accommodation properties of the eye. As objects move closer to a young, properly functioning eye, the effects of ciliary muscle contraction and zonular relaxation allow the lens of the eye to change shape, and thus increase its optical power and ability to focus at near distances. This accommodation can allow the eye to focus and refocus between near and far objects.
Presbyopia normally develops as a person ages, and is associated with a natural progressive loss of accommodation. The presbyopic eye often loses the ability to rapidly and easily refocus on objects at varying distances. The effects of presbyopia usually become noticeable after the age of 45 years. By the age of 65 years, the crystalline lens has often lost almost all elastic properties and has only limited ability to change shape.
Along with reductions in accommodation of the eye, age may also induce clouding of the lens due to the formation of cataracts. Cataracts may form in the hard central nucleus of the lens, in the softer peripheral cortical portion of the lens, or at the back of the lens. Cataracts can be treated by the replacement of the cloudy natural lens with an artificial lens. An artificial lens replaces the natural lens in the eye, with the artificial lens often being referred to as an intra-ocular lens or “IOL”.
A variety of technologies have been developed to enhance the ability of IOLs to facilitate viewing. Multifocal IOLs may, for example, often rely on a diffractive optical surface to direct portions of the light energy toward differing focal distances, thereby allowing the patient to clearly see both near and far objects. Alternative diffractive multifocal ophthalmic lenses (including contact lenses or the like) have been proposed for treatments of presbyopia without removal of the natural crystalline lens. Diffractive optical surfaces, either monofocal or multifocal, may also be configured to provide reduced chromatic aberrations.
Like other lenses, diffractive monofocal and multifocal lenses can make use of a material having a given refractive index and a surface curvature to provide a refractive power. Diffractive lenses also have a diffractive profile which confers the lens with a diffractive power that contributes to the overall optical power of the lens. The diffractive profile is typically characterized by a number of diffractive zones. The diffractive power is related to the properties of these zones, for instance their number, shape, size and position. When used for ophthalmic lenses these zones are typically annular lens zones, or echelettes, spaced about the optical axis of the lens. Currently used echelettes may typically be defined by a primary zone, a secondary zone between the primary zone and a primary zone of an adjacent echelette, and an echelette geometry. The echelette geometry includes limiting inner and outer diameters and a shaped or sloped profile. Secondary zones may describe the situation where the theoretical primary zone is a discontinuous function, leading to discrete steps in the profile height. Secondary zones may be introduced to solve the manufacturing issue of making sharp corner in a surface, and/or to reduce possible light scatter from sharp corners. The overall profile may be characterized by an echelette height or step height between adjacent echelettes. The relative radial spacing of the echelettes largely determine the power(s) of the lens and the step height of the secondary zones largely determines the light distribution between the different add powers. Together, these echelettes define a diffractive profile, often saw-toothed or stepped, on one of the surfaces of the lens.
A multifocal diffractive profile of the lens can be used to mitigate presbyopia by providing two or more optical powers, for example, one for near vision and one for far vision. These lenses may be in the form of a multifocal contact lens, most commonly a bifocal contact lens. The lenses may also take the form of an intraocular lens placed within the capsular bag of the eye, replacing the original lens.
Although monofocal and multifocal diffractive ophthalmic lenses have greatly improved the quality of vision for many patients, additional improvements would still be beneficial. For example, some pseudophakic patients may experience effects such as halos and scatter. Therefore, monofocal and multifocal diffractive lenses having diffractive profiles resulting in reduced scatter (and thus an improved quality of vision) may be beneficial. For multifocal lenses, along with directing portions of the incident light energy at focal distances suitable for near and far viewing, diffractive optics may also direct significant light energy at other non-viewing foci, which can contribute to unwanted light-related visual phenomenon experienced by the patient (dysphotopsia). Having non-viewing foci of diffractive optics of multifocal lenses cannot be completely avoided. However, diffractive multifocal lenses having diffractive profiles which optimize the light energy distribution between viewing and non-viewing foci to improve quality of vision would also be beneficial. Controllably varying light distributions over the diffractive profile may also provide advantages, so that diffractive multifocal lenses having diffractive profiles which vary light distribution over the profile may be desirable.